In this photo taken on April 27, 2011, state police officers patrol a highway between Ciudad Victoria and Matamoros, Mexico. A total of 183 bodies have been found in mass graves near San Fernando, most of them were presumably people kidnapped from buses traveling between Ciudad Victoria, capital of Tamaulipas state, and the border town of Matamoros, according to authorities.

US Customs and Border Protection recently released data showing the number of those arrested trying to cross the US-Mexico is down sharply. There were 447,731 undocumented immigrants arrested in fiscal year 2010, reported CNN. That is a 58 percent decrease from fiscal year 2006.

Officials say that the number of agents along the border, which doubled during the same time frame, has played a preventive role.

Migrants, mostly from Central America, have long talked about the perils of traversing Mexico. As we reported in July 2007 from Tapachula – along Mexico’s southern border – migrants, even children, have always faced robbery, threats, and extortion from smugglers, corrupted immigration officials, and common criminals.

But stolen cash and even beatings were the kinds of risks poor migrants were willing to take.

Now, anecdotally at least, they are becoming much more cautious.

Last summer, a photographer and I visited the town of Tultitlan north of Mexico City. It is an industrial crossroads where migrants switch trains en route to the US. Several of them told us of the dangers they faced, big and small. One man from Nicaragua, Juan Palacios, was traveling with a friend who was kidnapped while waiting for a train. Mr. Palacios escaped the same fate, and made it to Tultitlan where he refused to go further.

This was right before the news of the massacre of 72 migrants last August in northern Mexico, on a ranch across the border from Texas, rocked Mexico. The migrants, mostly from Central America, were allegedly snatched off a bus and killed by the notorious Zetas drug-trafficking gang after refusing to work as recruits.

This spring, reports of missing bus passengers began surfacing in Tamaulipas. Weeks later mass graves were found, with some 200 bodies so far found in this one area alone. It is unclear how many of them are migrants. But a group of rescued migrants who had been kidnapped recently claimed that immigration officials delivered them to drug groups.

As drug crime grows, it seems, the shakedown has turned into something far riskier.

The institution’s head said they will also resort to lie detector tests to ensure a clean institution.

But the police have also been undergoing a series of confidence testing since Mexican President Felipe Calderón took office promising to reform the police, and that has done little to restore citizen faith in their cops. In fact, among the first arrests in the mass graves case of Tamaulipas? The municipal police.